There are a number of different technologies which can be used to provide a touch-sensitive surface and examples include resistive touch-screens, capacitive touch-screens and touch-screens which rely on optical sensing (e.g. using frustrated total internal reflection). Both resistive touch-screens and capacitive touch-screens can be designed to detect the positions of one or more fingers on the surface. Optical multi-touch tables, which use a camera/projector system or sensor-in-pixel technology, have the ability to sense multi-touch user input over a large sensing area. However, such tables are large, have rigid form-factor limitations (because of the optical arrangement) and a high power consumption.